Tim Kuniskis, head of the Fiat brand in the United States, said the Custom Shop would add parts that will fall under the Fiat warranty and can be bundled into dealership financing. He unveiled the program at the SEMA show. The production car will be built at the Fiat assembly plant, then sent to the custom shop for final changes.

The list of options initially will be limited to about 60 – items such as graphics packages, roof racks and aero kits. Also available are leather seats in Pop and Sport trim levels.

"We're going to start slow," Kuniskis said in an interview. "We want to make sure it's perfect."

But within a year or so, Fiat hopes to enlarge the list to more than 150 parts, including emissions-compliant performance modifications such as cold air intakes and cat-back exhausts.

Kuniskis did not have an average dollar figure for the amount of customization that 500 owners install on their cars. But dealers have told him that many customers order aftermarket parts, and that Chrysler's Mopar parts division doesn't play a big enough part in those purchase decisions.

The process is similar to the one used by Toyota's Scion brand, which installs custom-ordered accessories at a port facility before vehicles are sent to dealerships.

A custom-ordered car will require the customer to wait nearly two months. A car ordered today will be built about one month later, then require 21 days to ship to the dealership.